Electrolytic copper foil

ABSTRACT

Provided is an electrolytic copper foil having a surface roughness Rz of 2.0 μm or less, wherein a foil thickness difference in the width direction is 1.5% or less. Also provided is the electrolytic copper foil, wherein the foil thickness difference in the width direction is 1.3% or less. Further provided is the electrolytic copper foil, wherein a variation in the roughness in the width direction (Rzmax−Rzmin)/Rzavg is 15% or less. An object of the present invention is to provide an electrolytic copper foil having low surface roughness, wherein the formation of an “elongation wrinkle” and a discolored streak along the length direction is suppressed by allowing the thickness to be uniform in the width and length directions.

TECHNICAL FIELD

The present invention relates to an electrolytic copper foil, inparticular relates to an electrolytic copper foil having a lowroughness.

BACKGROUND

In general, a device for manufacturing an electrolytic copper foilcomprises a metal cathode drum and an insoluble metal anode (anode), themetal cathode drum being rotatable and having a mirror polished surface,the insoluble metal anode being arranged at approximately lower half ofthe metal cathode drum and surrounding the metal cathode drum. A copperfoil is continuously manufactured with the device by flowing a copperelectrolytic solution between the cathode drum and the anode, applyingan electrical potential between these to allow copper to beelectrodeposited on the cathode drum, and detaching an electrodepositedcopper from the cathode drum when a predetermined thickness is obtained.

A copper foil obtained as described above, which is generally called araw foil, is used for a copper foil for a negative electrode material oflithium batteries, a copper foil for a printed wiring board and the likeas it is or after surface treatment.

FIG. 1 shows a schematic diagram of the conventional device formanufacturing a copper foil. The device for manufacturing a copper foilcomprises Cathode drum 1 provided in an electrolytic bath (not shown)containing an electrolytic solution. Cathode drum 1 rotates under thecondition where it is immersed partially (approximately lower half) intothe electrolytic solution.

Insoluble metal anode (Anode) 2 is provided such that it surrounds thelower half of the outer circumference of Cathode drum 1. Gap 3 separatesCathode drum 1 and Anode 2 at a certain distance such that theelectrolytic solution flows between the two. Two anode plates areprovided as shown in FIG. 1

As shown in FIG. 1, the electrolytic solution supplied from a lower partpasses through Gap 3 between Cathode drum 1 and Anode 2, and overflowsfrom an upper edge of Anode 2 to further circulate. A predeterminedvoltage can be maintained between Cathode drum 1 and Anode 2 through arectifier.

As Cathode drum 1 rotates, a thickness of copper electrodeposited fromthe electrolytic solution increases. When a thickness equal to or abovea certain value is obtained, raw foil 4 is detached and continuouslyrolled up. The electrolytic copper foil manufactured as described abovehas a rough surface having a certain degree of roughness on the sideexposed to the electrolytic solution, and a glossy surface on theopposite drum side.

A “wrinkle” has not been a significant problem for the raw foilmanufactured as described above when it has a thick foil thickness and alarge surface roughness. However, in recent years, an “elongationwrinkle” in a copper foil is becoming a problem because a foil becomesthinner and the roughness becomes lower.

After extensively studying a variation in the foil weight in the widthdirection for a conventional electrolytic copper foil in order to findwhat causes the “elongation wrinkle,” the present inventors have foundthat a position where an elongation wrinkle (pocket elongation) isdeveloped shows a variation in foil weight as shown in FIG. 2.

A variation in weight means a variation in a plate thickness. When aplate thickness is thin and a surface roughness is low, the developmentof pocket elongation becomes significant due to the variation in theplate thickness.

This appears to cause the problem. However, a uniform plate thicknesshas to be considered across the width and length directions, namely, afilm thickness over the entire surface of a copper foil has to beconsidered. In the process of manufacturing an electrolytic copper foilas described above, the plate thickness is very difficult to beprecisely controlled, and in particular, a more uniform plate thicknessis not easily obtained in the case of a thin foil.

In a case where a small gap between a cathode drum and an anode ismaintained while an electrolytic solution flows into the gap to allowelectrodeposition, even a device designed for achieving uniformity mayoften cause a certain variation in a film thickness due to the issuesspecific to a manufacturing device and operating conditions.

Note that so far the present applicant has made many proposals forsolving the problem of a uniform plate thickness in which split anodesare provided at a portion of the anode in the copper foil rolling-upside, and an amount of electric power supplied to these split anodes isindividually controlled to arbitrarily adjust a thickness of a copperfoil in the width and length directions. Then many of those are patented(see Patent Literature 1, Patent Literature 2, Patent Literature 3,Patent Literature 4 and Patent Literature 5; Note that the patentees orapplicants of these patents have been changed, but all were done by thepresent applicant). As of today, these are effective.

Further, the technologies which decrease a surface roughness (PatentLiterature 6, Patent Literature 7, Patent Literature 8, PatentLiterature 9) are also proposed. Each of these is an effective patentand is excellent as a technology at the time. Particularly, theroughness of the rough surface of an electrolytic copper foil hasreached Ra of 0.1 μm or less and Rz of 2.0 μm or less.

However, in a case where split anodes are provided at a portion of theanode in the copper foil rolling-up side, and an amount of electricpower supplied to these split anodes is individually controlled as inthe above mentioned patent literatures in order to achieve a thin platethickness and a lower surface roughness as well as a uniform thicknessin the width and length directions, a problem of an observed discoloredstreak along the length direction is not solved. Therefore the problemremains to be solved.

-   Patent Literature 1: Japanese Patent No. 2506573-   Patent Literature 2: Japanese Patent No. 2506574-   Patent Literature 3: Japanese Patent No. 2506575-   Patent Literature 4: Japanese Patent No. 2594840-   Patent Literature 5: Japanese Patent No. 3416620-   Patent Literature 6: International Publication No. WO2005/010239-   Patent Literature 7: Japanese Patent Laid-Open No. 2004-107786-   Patent Literature 8: International Publication No. WO2004/055246-   Patent Literature 9: International Publication No. WO2004/059040

SUMMARY OF THE INVENTION Technical Problem

An object of the present invention is to provide an electrolytic copperfoil having a low surface roughness, having a uniform thickness in thewidth and length directions, but having no “elongation wrinkle,” whereinthe formation of a discolored streak along the length direction issuppressed.

Solution to Problem

The present inventors have found that the development of an “elongationwrinkle” is caused by a variation in the thickness in the width andlength directions and that a supplementary electrode can effectivelycontrol the variation in thickness of a copper foil. Further, thepresent inventors have found that a copper foil having no discoloredstreak along the length direction can be obtained by appropriatelyarranging the supplementary electrode.

Accordingly, the present invention provides: 1) An electrolytic copperfoil having a surface roughness Rz of 2.0 μm or less, wherein a foilthickness difference in a width direction is 1.5% or less, and nodiscolored streak along the length direction is present on a surface ofthe electrolytic copper foil;

2) The electrolytic copper foil according to 1), wherein the foilthickness difference in the width direction is 1.3% or less;3) The electrolytic copper foil according to 1) or 2), wherein avariation in the roughness in the width direction (Rzmax−Rzmin)/Rzavg is15% or less.

The present invention provides the following excellent advantageouseffects: the present invention does not cause an “elongation wrinkle” atthe time of rolling up, and can provide a copper foil having noobservable discolored streak along the length direction even in the caseof an electrolytic copper foil having a low surface roughness. Inparticular, since the foil has a low surface roughness and a smallvariation in the foil thickness, the foil is effective for a copper foilfor a negative electrode material of lithium batteries, and, forexample, can be applied to a copper foil for a negative electrodematerial of lithium batteries requiring a tensile strength of 50 to 70kg/mm² and an elongation of 5 to 9%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic side view (a cross-sectional view) of a devicefor manufacturing an electrolytic copper foil comprising a cathode drumand an anode.

FIG. 2 is a graph showing a variation in the foil weight indicating anelongation wrinkle (pocket elongation) in the width direction obtainedby the conventional method of manufacturing an electrolytic copper foil.

FIG. 3 is an image showing elongation wrinkles (pocket elongation) inthe width direction obtained by the conventional method of manufacturingan electrolytic copper foil.

FIG. 4 is a schematic side view (a cross-sectional view) showing anarrangement of a drum, anodes and a supplementary split anode in adevice for manufacturing an electrolytic copper foil according to thepresent invention adapted from the conventional device.

FIG. 5 is a schematic view showing the arrangement of the drum, theanode and the supplementary split anode seen from the supplementarysplit anode side arranged in the front side of the device according tothe present invention.

FIG. 6 is a diagram illustrating a method of measuring the weight of thethickness in the width direction of an electrolytic copper foil and thethickness in the drum circumference direction of the foil.

FIG. 7 shows graphs showing a variation in the foil weight of thethickness in the width direction and the thickness in the drumcircumference direction in the method of manufacturing an electrolyticcopper foil according to the present invention.

FIG. 8 shows graphs showing a variation in the foil weight of thethickness in the width direction and the thickness in the drumcircumference direction in the conventional method of manufacturing anelectrolytic copper foil.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a graph showing a variation in the foil weight indicating anelongation wrinkle (pocket elongation) in the width direction obtainedby the conventional method of manufacturing an electrolytic copper foil.As shown in FIG. 2, a pocket elongation has occurred at the centralsection in the width of a copper foil.

The present inventors have found that the development of an “elongationwrinkle” is caused by a variation in the plate thickness (a variation inthe foil weight) of an electrolytic copper foil in the width directionas shown in FIG. 2. After studying the variation in the plate thickness,the present inventors have found that the development of an elongationwrinkle (pocket elongation) can be suppressed when a foil thicknessdifference in the width direction is 1.5% or less. Further, morepreferably, a foil thickness difference in the width direction is 1.3%or less.

As described in the Patent Literatures, a supplementary electrodeprovided at the rolling-up side (the rear side) will provide a moreuniform plate thickness. However, in the case of a copper foil having alow degree of roughness, discoloring on a surface of a copper foil willbe significant.

In view of this, the present invention is characterized in that asupplementary split electrode is provided at the rolling-up side (therear side) and the opposite side (the front side), and when a variationin thickness is detected in advance in a device for manufacturing anelectrolytic copper foil and the supplementary split electrode in thefront side is used for adjustment, a copper foil having a uniform platethickness, having a low degree of roughness, but having no discoloringin the rolling-up side can be manufactured. Further, more preferably, afoil thickness difference is 1.5% or less even in the overall variationincluding the length direction (the drum circumference direction).

Note that the surface roughness of a copper foil is preferably 2.0 μm orless in Rz. More preferably, it is 1.6 μm or less. Although the cause ofdiscoloring is not cleared up, concerning copper layer electrodepositedparticles to be adjusted by the supplementary split electrode, since thestate of copper layer electrodeposited particles formed differs amongthe individual split electrodes, when the thickness is adjusted at therear side as described in the Patent Literatures, a final plating layerwill be formed by the supplementary split electrodes, which results inthe variation of plating adherence patterns (roughness) among thesupplementary split electrodes since each has different surface stateamong the split electrodes, thereby developing an unwanted discoloredstreak on a surface of the copper foil.

However, the adjustment at the early stage of copper layerelectrodeposition using the supplementary split electrode provided inthe front side and electrodeposited particles subsequently formed by theanode can make up for subtle differences in the patterns of the copperlayer electrodeposited particles formed by the supplementary splitelectrode, resulting in a preferred state of a uniform surface.Specifically, for the roughness which does not cause discoloring on asurface of a copper foil, a variation in the roughness in the widthdirection (Rzmax−Rzmin)/Rzavg is 15% or less.

That is, the variation in the roughness in the width direction(Rzmax−Rzmin)/Rzavg can be controlled to be 15% or less by providing asupplementary split electrode in the front side.

Such an electrolytic copper foil and a method of manufacturing thereofwill be described specifically below. A basic structure of a device formanufacturing an electrolytic copper foil according to the presentinvention is shown in FIG. 1. As shown in FIG. 1, it comprises Cathodedrum 1 and Anode 2, Cathode drum 1 being rotatable, Anode 2 having anarc-like shape, opposing to Cathode drum 1 and surrounding a portion ofthe circumference (approximately lower ¼).

An electrolytic bath contains a copper sulfate solution to be used as acopper electrolytic solution. The concentration, temperature, pH and thelike of the copper electrolytic solution are adjusted to perform goodelectrodeposition and the copper electrolytic solution is circulated andreused. A conventional electrolytic solution can be used as the presentelectrolytic solution.

Cathode drum 1 is immersed partially in the electrolytic solution androtated clockwise as shown in FIG. 1. As described above, Anode 2 isseparated from the surface of Cathode drum 1 by a certain distance, and,for example, placed around Cathode drum 1 in an arc-like fashion.

Cathode drum 1 uses, for example, a stainless steel or titaniumrotatable cylindrical body. Anode 2 uses an insoluble anode, which ismade of lead, a lead-antimony alloy, a silver-lead alloy, an indium-leadalloy and the like. A material generally called DSE or DSA in whichplatinum group or an oxide thereof is coated on a valve metal such astitanium can be used.

Anode 2 is shown in pairs (A1, A2) in FIG. 1, but two or more pieces maybe used so that Cathode drum 1 is covered over. The gap between Cathodedrum 1 and Anode 2 is usually kept in a fixed position in the rangebetween 2 and 100 mm or less. Although a smaller gap results in a lessamount of electricity, a plate thickness and quality are difficult to becontrolled. Thus, the above range is preferred.

The gap between Cathode drum 1 and Anode 2 serves as a flow passagewayof an electrolytic solution. As shown in FIG. 1, an electrolyticsolution supplied via a pump in the bath passes through Gap 3 betweenCathode drum 1 and Anode 2, and overflows from the upper edge of Anode2.

A predetermined voltage can be maintained between Cathode drum 1 andAnode 2 via a rectifier. The thickness of copper electrodeposited fromthe electrolytic solution increases on Cathode drum 1 as Cathode drum 1rotates. As shown in FIG. 1, when a certain thickness is obtained, Rawfoil 4 is detached from Cathode drum 1, and continuously rolled up witha roll-up unit (not shown).

Furthermore, as shown in FIG. 4, the device for manufacturing anelectrolytic copper foil of the present invention comprisesSupplementary split anode B as an anode for uniformity at the side wall(upper edge) of Anode 2 in the opposite side (the front side) from thecopper foil rolling-up side (the rear side), Supplementary split anode Bbeing opposed to Cathode drum 1.

That is, in a device for manufacturing an electrolytic copper foil,comprising Cathode drum 1 which is immersed partly in a copperelectrolytic solution and rotatable; Anode 2 which is opposed to Cathodedrum 1 and surrounds a part of the circumference thereof; a unit forelectrodepositing copper on Cathode drum 1 by flowing a copperelectrolytic solution between Cathode drum 1 and Anode 2; and a unit fordetaching an electrodeposited copper foil from the cathode drum,provided are Supplementary split anode B opposed to Cathode drum 1located at the side wall of Anode 2 in the opposite side from the copperfoil rolling-up side; and a unit for individually controlling an amountof electricity supplied to Anode 2 and Supplementary split anode B.

Supplementary split anode B is further separated in the width direction,and an amount of electricity can be individually controlled for each.Further, Anode 2 may comprise two anodes: Anode A1 and A2. In this case,a unit can be provided to individually control an amount of electricitysupplied to Supplementary split anode B provided at the side wall (upperedge) of Anode A1 in the opposite side from Anode A2 located in thecopper foil rolling-up side of Anode A1 and A2.

FIG. 5 is a schematic view showing the arrangement of Cathode drum 1,Anode A1 and Supplementary split anode B seen from the side of thesupplementary split anode. The length in the width direction ofSupplementary split anode B can be approximately the same as that ofAnode A1, but the length can be adjusted as appropriate. Further, it ispreferably attached to Anode A1 for secure holding in an easilydetachable fashion using, for example, a bolt.

An amount of electricity for Supplementary split anode B and Anode A1 isallowed to be individually controlled. Therefore, Supplementary splitanode B is attached to Anode A1 via a fixing member capable ofelectrical insulation.

The amount of electricity supplied to Supplementary split anode B isadjusted so that an electrolytic copper foil is manufactured having alow surface roughness and a uniform thickness in the width and lengthdirections, and the formation of an “elongation wrinkle” and adiscolored streak along the length direction is suppressed.

Further, an advantage is that the improvement in a device by providingSupplementary split anode B can be easily implemented in an existingdevice for manufacturing an electrolytic copper foil.

When the device for manufacturing an electrolytic copper foil of thepresent invention is used for electrolysis, a foil thickness differencein the width direction of an electrolytic copper foil of 1.5% or lesscan be achieved. This solves the problem which has been difficult tocontrol so far. That is, by providing a supplementary split electrode inthe front side, a variation in the plate thickness (a change in foilweight) in the width direction of an electrolytic copper foil can becontrolled, a foil thickness difference in the width direction of 1.5%or less can be achieved, and the development of an elongation wrinkle(pocket elongation) can be suppressed.

Note that a condition for the present invention is a low roughnesscopper foil having a surface roughness Rz of 2.0 μm or less. Morepreferably, it is 1.6 μm or less.

As described below, a foil thickness difference in the width directionof 1.5% or less allows both a uniform thickness in the width directionand a uniform thickness in the drum circumference direction at the sametime. The supplementary split electrode serves to adjustelectrodeposited particles subsequently formed in the early stage ofcopper layer electrodeposition, and continues to perform its function inturn. Therefore, a uniform thickness in the width direction inevitablyresult in a function to cause a uniform thickness of a copper layeralong the drum circumference direction, i.e., across the lengthdirection of the copper foil.

Further, by providing a supplementary split electrode in the front side,the influence from the copper layer electrodeposited particles formed bythe supplementary split electrode will be avoided, allowing a smallvariation in the roughness in the width direction since electrodepositedparticles are uniformly formed by the anode on the entire surface overthe electrodeposited particles previously formed by the supplementarysplit electrode. That is, (Rzmax−Rzmin)/Rzavg can be controlled to be15% or less.

Next, specific examples of the present invention will be described belowin comparison with the conventional art. Note that the specific examplesare merely examples, and the present invention is not limited to theseexamples. That is, all aspects or modifications not described inExamples which are within the scope of the spirit of the presentinvention are encompassed.

With regard to Examples 1 to 5, a device comprising Supplementary splitanode B provided at the side wall (upper edge) of Anode A1 in theopposite side from Anode A2 in the copper foil rolling-up side of Anode2 and a unit for individually controlling an amount of electricitysupplied to Supplementary split anode B was used to produce electrolyticcopper foils with various thicknesses.

In contrast, with regard to Comparative Examples 6 to 10, thesupplementary split anode was not provided, with regard to ComparativeExamples 11 to 15, the supplementary split anode was provided at thecopper foil rolling-up side as in the Patent Literatures 1 to 3 toproduce electrolytic copper foils with various thicknesses.

The weight (change) associated with a variation in the thickness in thewidth direction and the thickness in the drum circumference direction(the length direction of a copper foil) of an electrolytic copper foilcan be measured, for example, as shown in FIG. 6. That is, in the caseof 36 point gravimetry, a reference point is marked every 10° along thedrum circumference direction. Next, the sample was cut at every 3reference points (186 mm), and both ends of each cut sample were furthercut by 20 mm.

Next, this cut foil is folded 4 times, and divided into 16. This ispunched to a 100 mm square sheet, and the weight of this 100 mm squaresheet is measured. Further, the electrodeposited side of each sheet ismeasured for a surface roughness Rz. The mean value of Rz for each sheetis called Rzavg, and the maximum value and the minimum value among themeasured values are called Rzmax and Rzmin, respectively.

Measurements of the weight of the thickness in the width direction of afoil and the thickness in the drum circumference direction of the foilcan be measured by other methods, but this method is an actuallysuitable gravimetric method. The gravimetric measurements shown in FIGS.7 and 8 are performed using this approach.

Further, the development of an elongation wrinkle was evaluated at thetime of rolling-up, and the presence of a discolored streak wasevaluated by the cut sample at the end. Note that one of ordinary skillin the art can easily determine the presence of a discolored streak bycomparing a base region with a discolored region in the same samplehaving a discolored streak. The results are shown in Table 1.

TABLE 1 Variation in the Nominal Supplementary thickness in theElongation No. thickness split anode width direction (%) wrinkleDiscoloring Example 1 35 μm Front side 0.89 not found not found 2 20 μmFront side 0.87 not found not found 3 12 μm Front side 0.88 not foundnot found 4 10 μm Front side 0.79 not found not found 5  8 μm Front side0.83 not found not found Comparative 6 35 μm — 1.75 found not foundExample 7 20 μm — 1.80 found not found 8 12 μm — 1.77 found not found 910 μm — 1.79 found not found 10  8 μm — 1.74 found not found 11 35 μmRear side 0.91 not found found 12 20 μm Rear side 0.85 not found found13 12 μm Rear side 0.86 not found found 14 10 μm Rear side 0.82 notfound found 15  8 μm Rear side 0.84 not found found

FIG. 7 shows graphs showing a variation in the foil weight of thethickness in the width direction and the thickness in the drumcircumference direction in Example 1. According to this, the variationin the foil weight of both the thickness in the width direction and thethickness in the drum circumference direction showed a small variationof 0.05 g/dm² or less. In Examples 2 to 5, the variation in the foilweight of both the thickness in the width direction and the thickness inthe drum circumference direction also showed a small variation.

The variation (%) in the thickness in the width direction of a copperfoil, namely, the foil thickness difference in the width direction of acopper foil is shown in Table 1. In Examples 1 to 5, the variation wasin the range between 0.79 and 0.89%. As a result, an “elongationwrinkle” did not occur even at the time of rolling-up in Examples 1 to5. Further, no discolored streak was found in all of Examples.

On the other hand, FIG. 8 shows graphs showing a variation in the foilweight of the thickness in the width direction and the thickness in thedrum circumference direction in the case of Comparative Example 6, i.e.in the case where Supplementary split anode is not provided.

As shown in FIG. 8, the variation in the foil weight of both thethickness in the width direction and the thickness in the drumcircumference direction shows a large variation of almost 0.10 g/dm².

In Comparative Examples 7 to 10, the variation in the foil weight ofboth the thickness in the width direction and the thickness in the drumcircumference direction also showed a large variation. As shown in Table1, in Comparative Examples 6 to 10, the variation in the thickness inthe width direction of a copper foil, namely, the foil thicknessdifference in the width direction of a copper foil is in the rangebetween 1.74 and 1.80%, which is larger than that in Examples. InComparative Examples 6 to 10, as a result, an “elongation wrinkle”occurred at the time of rolling-up. Note that no discolored streak alongthe length direction (in the drum circumference direction) of a copperfoil was observed. The results are also shown in Table 1.

In Comparative Examples 11 to 15, in which a supplementary split anodewas provided in the rear side (in the copper foil rolling-up side) byway of contrast, the variation in the foil weight of both the thicknessin the width direction and the thickness in the drum circumferencedirection showed a variation as small as those in Examples. That is, asshown in Table 1, the variation in the thickness in the width directionof a copper foil, namely, the foil thickness difference in the widthdirection of a copper foil was in the range between 0.82 and 0.91%,showing no “elongation wrinkle” at the time of rolling-up. However, adiscolored streak along the length direction, i.e. the drumcircumference direction) of a copper foil was observed. The results arealso shown in Table 1. This reveals that providing a supplementary splitanode in the rear side is not expedient.

As described above, the advantages according to the present inventionare as follows: the foil thickness precision can be improved; thedevelopment of an “elongation wrinkle” can be suppressed by a uniformfoil thickness in the width and length directions; and the developmentof a discolored streak along the length direction can be suppressed evenif a surface roughness is low.

INDUSTRIAL APPLICABILITY

The advantageous effects of the present invention are able to suppressthe development of an “elongation wrinkle” by a uniform thickness in thewidth and length directions and the development of a discolored streakalong the length direction even in an electrolytic copper foil having alow surface roughness. Therefore, it can be used as a copper foil for anegative electrode material of lithium batteries, and a copper foil fora printed wiring board in which a thin copper foil suitable for a denserelectronic circuit, a narrower circuit width and multi-layering isrequired. In particular, it is useful for a copper foil for a negativeelectrode material of lithium batteries in which a tensile strength of50 to 70 kg/mm², and an elongation of 5 to 9%, for example, are requiredsince it has a low surface roughness and a small variation in the foilthickness.

REFERENCES SIGNS LIST

-   1 Cathode drum-   2 Anode (A1, A2)-   3 Gap-   4 Raw foil

1. An electrolytic copper foil having a surface roughness Rz of 2.0 μmor less, wherein a foil thickness difference among sixteen places in awidth direction is 1.5% or less, the electrolytic copper foil is cut atboth ends in the width direction by 20 mm and folded four times anddivided into sixteen to measure the foil thickness difference in thewidth direction, no discolored streak is present along a lengthdirection on a surface of the copper foil, and an elongation wrinkle isnot developed.
 2. The electrolytic copper foil according to claim 1,wherein the foil thickness difference among the sixteen places in thewidth direction is 1.3% or less.
 3. The electrolytic copper foilaccording to claim 1, wherein a variation in the roughness in the widthdirection (Rzmax−Rzmin)/Rzavg is 15% or less.
 4. The electrolytic copperfoil according to claim 1, wherein the foil thickness difference amongthe sixteen places in the width direction is 0.89% or less.
 5. Theelectrolytic copper foil according to claim 4, wherein a variation inthe surface roughness in the width direction (Rzmax−Rzmin)/Rzavg is 15%or less.
 6. A method of manufacturing an electrolytic copper foil,comprising the steps of: flowing a copper electrolytic solution betweena rotating cathode drum and an anode opposed to the cathode drum toallow copper to be electrodeposited on a surface of the cathode drum;providing a supplementary split anode only along a front side of thedrum; individually controlling an amount of electricity provided to eachof a plurality of split anodes of the supplementary split anode, theplurality of split anodes being separated in a width direction of thedrum; and detaching an electrodeposited copper foil from the cathodedrum.
 7. The method according to claim 6, wherein the electrodepositedcopper foil is produced such that the copper foil has a surfaceroughness Rz of 2.0 μm or less and a foil thickness difference acrossthe width direction of 1.5% or less, and no discolored streak is presentalong a length direction on a surface of the copper foil.
 8. The methodaccording to claim 7, wherein the foil thickness difference in the widthdirection is 1.3% or less.
 9. The method according to claim 8, wherein avariation in the surface roughness in the width direction(Rzmax−Rzmin)/Rzavg is 15% or less.
 10. The method according to claim 7,wherein a variation in the surface roughness in the width direction(Rzmax−Rzmin)/Rzavg is 15% or less.